Blacks are more likely to have an undiagnosed key risk factor for stroke and are more likely to have a stroke than whites, according to two studies presented at the American Stroke Association's International Stroke Conference 2010.

In two separate reports using data from the REGARDS (REasons for Geographic and Racial Differences in Stroke) study, researchers found significant racial and geographic disparities in stroke incidence and in receiving the recommended treatment to prevent stroke.

The REGARDS study enrolled 30,239 participants across the United States, age 45 or older, between January 2003 and October 2007 and continues to follow them for health events.

In the first analysis (Meschia, Abstract P160), researchers found that among 432 study participants (88 blacks; 344 whites) who had atrial fibrillation (AF), blacks were two-thirds less likely to know they had the disorder and three-fourths less likely to be treated with the gold standard of care, the blood thinner warfarin.

"These disparities are a problem," said James F. Meschia, M.D., the study's lead author and a neurologist at the Mayo Clinic in Jacksonville, Fla. "For patients who are able to take warfarin, it makes a huge difference. Stroke trials have shown that warfarin reduces the risk of stroke by 60 percent."

Meschia notes that warfarin is not for everyone, because of the risk of bleeding. AF, which affects more than 2.2 million Americans, occurs when one of the heart's upper chambers quivers and doesn't effectively pump blood out, which allows blood to pool and clot. These dangerous clots can cause stroke if they lodge in an artery in or leading to the brain. This research is also simultaneously published in Stroke: Journal of the American Heart Association.

"Because atrial fibrillation is such a powerful risk factor for stroke, these findings suggest that lower awareness of atrial fibrillation and reduced likelihood of treatment among blacks may place blacks at higher risk of a stroke, which in turn could contribute to the higher stroke mortality among blacks," Meschia said.

The healthcare system needs to better screen for and inform people about whether they have AF, and more study is needed to shed light on the causes of the disparity in warfarin treatment, he said.

In the second analysis (Howard, abstract P158), researchers provide the first national data describing racial and regional disparities in stroke incidence. Researchers reviewed data on about 26,580 REGARDS participants who had not had a stroke at baseline and documented 299 strokes during the almost five-year period.

More strokes occurred among blacks, men, older people and those living in the so-called "stroke belt" - in this study identified as: North Carolina, South Carolina, Georgia, Alabama, Arkansas, Louisiana, Tennessee and Mississippi, said Virginia J. Howard, Ph.D., the lead author.

She noted this information is important because the medical community has long known that blacks die at a higher rate from stroke than whites, but there has been little data explaining why. The analysis suggests that the higher rate of stroke in the African-American population may be one of the reasons.

"Certain subgroups are more at risk and need to pay serious attention to their risk factors to prevent stroke," said Howard, associate professor of epidemiology at the School of Public Health at the University of Alabama at Birmingham. "Sometimes people don't appreciate that you can prevent stroke rather than attribute it to running in the family or being part of the natural aging process.

"More concentrated prevention strategies must be focused on preventing the stroke from ever happening. This will require better access to care across all the United States but especially for hard-to-reach areas and for African Americans."

Editor's note: Learn more about the American Heart Association/American Stroke Association's advocacy efforts to address the ethnic and racial disparities in the diagnosis and treatment of stroke, the No. 3 killer of Americans. Visit www.strokeassociation.org/advocacy.

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